Dual fuel boiler with backflow-preventing valve arrangement

ABSTRACT

A dual fuel boiler has fuel delivery apparatus coupled to its burner section through a pressure regulator and operative to deliver to the burner section, from sources thereof, a selectively variable one of (1) a first fuel at a pressure greater than the pressure regulation setting of the pressure regulator, and (2) a second fuel at a pressure less than the pressure regulation setting, the second fuel having a Wobbe index greater that that of the first fuel. The first fuel is flowed to the burner section via a branch supply line in which first and second electromechanical two position, two-way, two position valves are installed in series in opposite normal flow orientations to thereby prevent backflow of the second fuel into the source of the first fuel.

BACKGROUND OF THE INVENTION

The present invention generally relates to combustion apparatus and, in a preferred embodiment thereof, more particularly relates to a specially designed dual fuel burner system for a fuel-fired heating appliance such as, for example, a boiler.

Dual fuel boilers have been supplied, primarily by power burner type boiler manufacturers, for many years. The ability to selectively operate a boiler, or other type of fuel-fired heating appliance, with one or the other of two different fuels (such as, for example, natural gas or propane) is desirable to provide operation if and when the primary fuel source is interrupted. Often the pricing of the primary fuel source can be discounted if the customer agrees to accept interruption of the fuel supply by the supplier when so requested. In this event, the customer simply switches to the secondary or “backup” fuel source until the source of primary fuel is re-established by the supplier.

Conventional power burner practices are (1) to have two separate burner heads that can be interchanged to accommodate the switch back and forth between the two different types of fuel, or (2) to have back-up fuels with essentially the same Wobbe indexes such as propane-air to back up natural gas. The first listed conventional design, of course, requires a mechanical modification to the overall burner structure each time that a different fuel is to be used to fire the boiler.

A desirably simplified technique for switching back and forth between two alternative fuel sources (a primary fuel source and an alternate or secondary fuel source) in a dual fuel boiler is illustrated and described in U.S. Pat. No. 6,904,873 to Ashton which is assigned to the same assignee as the assignee of this application, and which is hereby incorporated in its entirety herein by this reference.

In further developing the dual fuel boiler illustrated and described in U.S. Pat. No. 6,904,873 a goal was established to provide it with a modified primary fuel/secondary fuel switching system having a valving arrangement that even more effectively prevents secondary fuel back pressure from potentially contaminating the primary fuel source with secondary fuel.

SUMMARY OF THE INVENTION

In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, a specially designed dual fuel heating appliance is provided. The heating appliance is representatively a dual fuel boiler and comprises fuel burner apparatus having an inlet portion, and fuel delivery apparatus operative to deliver to the fuel burner apparatus a selectively variable one of a first fuel (representatively natural gas) from a source thereof, and a second fuel (representatively propane) from a source thereof.

The fuel delivery apparatus includes a main fuel supply line connected to the inlet portion of the fuel burner apparatus, a first fuel supply branch line connected to the main fuel supply line and connectable to the first fuel source, first valve apparatus connected in the first fuel supply branch line and being openable and closable to selectively permit and preclude flow of the first fuel therethrough, a second fuel supply branch line connected to the main fuel supply line and connectable to the second fuel source, and second valve apparatus connected in the second fuel supply branch line and being openable and closable to selectively permit and preclude flow of the second fuel therethrough.

According to a key aspect of the invention, the first valve apparatus includes first and second electromechanical two position, two-way valves connected in series, and in opposite normal flow orientations, in the first fuel supply branch line. When these two valves are closed, second fuel backpressure on one of the valves is added to the diaphragm closing spring force thereof to more positively preclude the pressurized second fuel from backflowing into and contaminating the first fuel source.

Preferably, the dual fuel heating appliance, which is illustrated in both single and multiple burner embodiments, additionally incorporates therein the relative first and second fuel pressure control technique disclosed in U.S. Pat. No. 6,904,873 which permits the use of either the first fuel or the second fuel, the first and second fuels having different Wobbe indexes, without modifying the supply orifice structure of the burner apparatus. To accomplish this, the fuel delivery system further includes a first pressure regulator through which both of the first and second fuels must flow to reach the burner apparatus, and a second pressure regulator through which only the higher Wobbe index fuel must flow to reach the burner apparatus, the pressure regulation setting of the first pressure regulator being higher than the pressure regulation setting of the second pressure regulator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a representative dual fuel-fired boiler embodying principles of the present invention;

FIG. 2 is a schematic diagram of a specially designed dual fuel delivery system utilized in the boiler;

FIG. 3 is a schematic diagram of a multi-burner version of the FIG. 2 fuel delivery system; and

FIGS. 4A and 4B are enlarged scale schematic cross-sectional views of the dashed area “4” in FIG. 2 and respectively illustrate one of the electromechanical valves in FIG. 2 in its de-energized, normally closed orientation and its energized, opened position.

DETAILED DESCRIPTION

Schematically illustrated in FIG. 1 is a fuel-fired heating appliance which embodies principles of the present invention and is representatively a dual fuel boiler 10. While a fuel-fired boiler is representatively illustrated, the heating appliance could be a variety of other types of dual fuel heating appliances such as, for example, a pool heater or other type of fuel-fired water heater, and principles of the present invention are not limited to boiler applications.

The dual fuel boiler 10 includes fuel burner apparatus 12 which is representatively of a non-aspirating type, and a combustion air blower 14 used to supply the fuel burner apparatus 12 with combustion air 16. According to a key aspect of the present invention, the dual fuel boiler 10 is provided with a specially designed fuel delivery system 18 which is operatively associated with the burner apparatus 12 and may be utilized to selectively supply to the burner apparatus 12 either a primary first fuel 20 (representatively natural gas) or a secondary fuel 22 (representatively propane) having a Wobbe index higher than that of the first fuel 20. First fuel 20 is supplied to the boiler 10 via a branch fuel supply line 24, and the second fuel 22 is supplied to the boiler 10 via a branch fuel supply line 26.

In FIG. 2 there is schematically shown a representative single burner version of the burner apparatus 12 and the fuel delivery system 18. The burner apparatus 12 is a single, non-aspirating type fuel burner 28 having incorporated therein, in an inlet head portion thereof, a fuel discharge orifice 30. According to a key aspect of the present invention, the fuel delivery system 18, compared to the fuel delivery system incorporated in the dual fuel boiler systems illustrated and described in U.S. Pat. No. 6,904,873, has an improved valving arrangement, later described herein, that more effectively prevents secondary fuel back pressure from potentially contaminating the primary fuel source with secondary fuel.

In addition to the branch fuel supply lines 24 and 26, the fuel delivery system 18 includes a main fuel supply line 32 coupled as shown to the branch fuel supply lines 24,26 and extending from its juncture therewith to the burner inlet fuel orifice 30. A manual shutoff valve 34 and a pressure regulator apparatus 36 are connected as shown in the main fuel supply line 32 between the branch supply lines 24,26 and the fuel discharge orifice 30.

As schematically and representatively illustrated, the pressure regulator apparatus 36 is a combination pressure regulator and safety or operating valve. Alternatively, the pressure regulator apparatus 36 may comprise separate pressure regulator and valve structures operatively connected in the main fuel supply line 32 upstream from the manual shutoff valve 34 without departing from principles of the present invention. A pressure regulator 38 is installed as shown in the second branch fuel supply line 26. Preferably, the pressure regulator 38 is a “lock-up” type regulator, of a conventional construction, which incorporates therein a check valve structure that prevents leftward fluid backflow through the regulator 38.

The improved valving arrangement of the fuel delivery system 18 also includes three electromechanical normally closed, two position, two-way, gas valves 40,42,44 of the solenoid/diaphragm type utilizing a linear motor output motion as later described herein. Valve 40 is connected in the branch fuel supply line 26 downstream of the pressure regulator 38, and valves 42,44 are connected in series in the branch fuel supply line 24, with valve 42 being upstream of the valve 44.

Manual shutoff valves (not shown) are connected in the branch fuel supply lines 24 and 26, respectively upstream of the pressure regulator 38 and the electromechanical valve 42. The manual shutoff valve 34 may be optionally installed, where shown, in addition to these non-illustrated manual shutoff valves.

Each of the valves 40,42,44 has a normal or intended internal flow direction as indicated by the arrow 46 thereon. When it is desired to supply natural gas to the boiler 10, the electromechanical valve 40 is left closed, and the electromechanical valves 42 and 44 are electrically opened to permit natural gas to flow to the burner 12 via the lines 24 and 32. When it is desired to supply propane to the boiler 10, the electromechanical valves 42 and 44 are closed and the electromechanical valve 40 is electrically opened to permit propane to flow to the burner 12 via the lines 26 and 32.

FIG. 4A cross-sectionally depicts the electromechanical valve 42 (which is configured similarly to the valves 40 and 44) in its de-energized normally closed orientation, and FIG. 4B cross-sectionally depicts the valve 42 in its energized or opened configuration. Like valves 40 and 44, valve 42 has an inlet end 48, an outlet end 50, and an internal flow passage 52 extending therethrough between the ends 48 and 50. Internal flow passage 52 extends through an orifice 54. When the valve 42 is in its normally closed FIG. 4A orientation, the orifice 54 is blocked by a closure diaphragm 56 which is coupled to the vertically movable core 58 of the solenoid portion of the valve and spring-driven downwardly against the top side of the orifice 54 to close it against gas flow therethrough. When the valve 42 is electrically energized to open it (see FIG. 4B), the solenoid core 58 is electrically driven upwardly to thereby open the orifice 54 and permit gas flow in either direction through the internal passage 52 between the valve's inlet and outlet ends 48,50.

According to a key aspect of the present invention, the electromechanical valves 42,44 connected in series in the natural gas branch supply line 24 are “oppositely” connected therein such that their normal flow arrows 46 are oppositely directed. Because of this unique opposite normal flow orientations of the electromechanical valves 42,44 in the branch line 24, when propane is being delivered to the boiler 10 via the branch supply line 26, propane back pressure on the natural gas valve 44 adds to the spring pressure on its diaphragm 56 so that such propane back pressure cannot lift the diaphragm off the orifice of valve 44 and permit propane backflow through the valve 44. With the valves 42,44 in such opposite normal flow orientations in the line 24, natural gas flowing rightwardly through the (opened) valves 42,44 sequentially passes through the normal inlet 48 of the valve 42, the normal outlet 50 of the valve 42, the normal outlet 50 of valve 44, and the normal inlet 48 of valve 44. Note that if valve 44 were omitted, the propane back pressure exerted on the diaphragm 56 of valve 42 would be exerted thereon in a direction opposite to that of its diaphragm closure spring, thereby potentially lifting the diaphragm and permitting undesirable propane backflow through the single electromechanical valve 42.

Natural gas pressure on valve 42 in its normally closed position (for example, when propane is being supplied to the boiler 10), adds to the closure force on the diaphragm of valve 42 to thereby more positively preclude natural gas flow rightwardly through the branch line 24. Natural gas backflow through the propane branch supply line 26 when the valve 40 is in its normally closed position, is prevented by the check valve structure in the pressure regulator 38, and by the diaphragm spring closure force within the valve 40.

By appropriately opening or closing the electromechanical valve 40, or the electromechanical valves 42 and 44, either the first fuel 20 or the second fuel 22 may be supplied to the burner 28 during firing thereof. AS in the case of the dual fuel boiler apparatus illustrated and described in U.S. Pat. No. 6,904,873, when the first fuel 20 is being supplied to the burner 28 the first fuel 20 is delivered to the pressure regulator apparatus 36 at a pressure higher than its pressure regulation setting, and when the second fuel 22 is being supplied to the burner 28 the second fuel 22 is delivered to the pressure regulator apparatus 36 at a pressure lower than its pressure regulation setting. Further, the pressures of the first and second fuels 20,22 as they reach the burner 28 are related to one another in a manner such that the firing rate of the burner 28 is essentially the same regardless of which of the fuels 20,22 is being delivered thereto. This advantageously eliminates the necessity of changing out the burner orifice 30 each time a switch is made from either of the fuels 20,22 to the other fuel.

Representatively, but not by way of limitation, the setting of the pressure regulator apparatus 36 is nominally 3.5″ W.C., the first fuel (by virtue of a non-illustrated upstream pressure regulator) is delivered to the oppositely connected electromechanical valves 42,44 at a pressure within the range of from about 7″ to about 14″ W.C., and the pressure regulator 38 is set to reduce the pressure of the second fuel 22 delivered to the electromechanical valve 40 to about 2.0″ W.C. Accordingly, for the fuel delivery system 18 illustratively depicted in FIG. 2, when the first fuel 20 is being supplied to the burner 28 the pressure regulator apparatus 36 reduces the pressure of the first fuel 20 that it receives to nominally 3.5″ W.C. for supply to the burner 28.

However, when the second fuel 22 is being supplied to the burner 28, the pressure regulator apparatus 36 does not regulate the pressure of the second fuel downwardly (since the second fuel is delivered to the pressure regulator apparatus 36 at a pressure lower than its setting), and the second fuel 22 is supplied to the burner 28 at a pressure of about 1.3″ W.C. due to the inherent valve and supply line pressure drops. Thus, the pressure of the first fuel 20 being supplied to the burner orifice 30 will be a function of the setting of the pressure regulator apparatus 36, while the pressure of the second fuel 22 being supplied to the burner orifice 30 will be a function of the pressure of the second fuel 22 upstream of the pressure regulator apparatus 36 and the inherent valve and supply line pressure drops.

AS can be seen, by simply adjusting the settings of the pressure regulating devices 36 and 38 the fuel delivery system 18 can be correspondingly adjusted to maintain the firing rate of the burner 28 at a substantially constant level when other combinations of fuels are coupled to the fuel delivery system for use with the burner 28.

FIG. 3 schematically illustrates modified burner apparatus 12 a and an associated modified fuel delivery system 18 a which may be alternatively incorporated in the dual fuel boiler 10 or other fuel-fired heating appliance. Instead of the single burner 28 defining the burner apparatus 12 shown in FIG. 2, the modified burner apparatus 12 a depicted in FIG. 3 comprises two pluralities of burners 28 a (representatively two groups of three burners 28 a). The modified fuel delivery system 18 a includes two branch fuel supply lines 32 a, each of which couples the main fuel supply line 32 to one of the two burner groups as shown. The modified fuel delivery system 18 a also includes two pressure regulating apparatuses 36 a, each of which is installed in one of the branch lines 32 a. Representatively, each of the two pressure regulator apparatuses 36 a has a setting equal to that of the single pressure regulator apparatus 36 shown in FIG. 2. In all other regards, the modified fuel delivery system 18 a is identical in construction and operation to the previously described fuel delivery system 18 shown in FIG. 2. AS in the case of the fuel delivery system 18, the pressure regulators 36 a are representatively set at nominally 3.5″ W.C., and the second fuel pressure regulator 38 is set to about 2.0″ W.C. Thus, by simply opening the valve 40, or the valves 42,44, the multiple burners 28 a may be operated at substantially equal firing rates using either of the two fuels 20 and 22 without the necessity of changing out any of the burner orifices 30 a.

The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims. 

1. A fuel-fired heating appliance comprising: fuel burner apparatus having an inlet portion; pressure regulator apparatus having an outlet portion coupled to said inlet portion of said fuel burner apparatus, and a predetermined pressure regulation setting; and fuel delivery apparatus coupled to said pressure regulator apparatus inlet portion and operative to deliver thereto a selectively variable one of (1) a first fuel, from a source thereof, at a pressure greater than said predetermined pressure regulation setting, and (2) a second fuel at a pressure lower than said predetermined pressure regulation setting, said fuel delivery apparatus including a fuel supply line communicated with said inlet portion of said fuel burner apparatus and through which one of said first and second fuels may be flowed, and first and second electromechanical two position, two-way valves connected in series in said fuel supply line in opposite normal flow orientations, said pressure regulator apparatus regulating the pressure of fuel discharged from its outlet portion only with respect to said first fuel, and said pressure regulator apparatus and said fuel delivery apparatus being coupled in a manner precluding said pressure regulation setting from being affected by which of said first and second fuels is being delivered to said pressure regulator apparatus.
 2. The fuel-fired heating appliance of claim 1 wherein: said fuel burner apparatus is of a non-aspirating type, and said fuel-fired heating appliance further comprises a blower operative to supply combustion air to said fuel burner apparatus.
 3. The fuel-fired heating appliance of claim 1 wherein: said fuel-fired heating appliance is a boiler.
 4. The fuel-fired heating appliance of claim 1 wherein: said first fuel is natural gas, and said second fuel is propane.
 5. The fuel-fired heating appliance of claim 1 wherein: said fuel delivery apparatus further includes a pressure regulator operative to reduce the pressure of the second fuel when it is being flowed to said fuel delivery apparatus.
 6. The fuel-fired heating appliance of claim 1 wherein: said fuel burner apparatus comprises a plurality of fuel burners, and said pressure regulator apparatus comprises a plurality of pressure regulators operatively coupled to said plurality of fuel burners.
 7. A fuel-fired heating appliance comprising: a fuel burner having an inlet orifice; a fuel delivery system for alternately supplying first and second fuels having different wobbe indexes to said inlet orifice at different pressures related to said different Wobbe indexes in a predetermined manner such that the firing rate of said fuel burner remains substantially the same, without changing said inlet orifice, regardless of which one of said first and second fuels is being supplied to said fuel burner, said fuel delivery system including: a fuel supply line communicated with said inlet orifice and through which one of said first and second fuels may be flowed, first and second electromechanical two position, two-way valves connected in series in said fuel supply line in opposite normal flow orientations, a first pressure regulator through which both of said first and second fuels must flow to reach said fuel burner, and a second pressure regulator through which only the higher Wobbe index fuel must flow to reach said fuel burner.
 8. The fuel-fired heating appliance of claim 7 wherein: said fuel-fired heating appliance is a fuel-fired boiler.
 9. The fuel-fired heating appliance of claim 7 wherein: said fuel burner is a non-aspirating type burner, and said fuel-fired heating appliance further comprises a blower operative to supply combustion air to said fuel burner.
 10. The fuel-fired heating appliance of claim 7 wherein: the pressure regulation setting of said first pressure regulator is higher than the pressure regulation setting of said second pressure regulator.
 11. A fuel-fired heating appliance comprising: non-aspirating type fuel burner apparatus having an orificed fuel inlet portion; blower apparatus for supplying combustion air to said fuel burner apparatus; a main fuel supply line structure coupled to said orificed fuel inlet portion; first pressure regulator apparatus connected in said main fuel line structure and having an inlet portion and a first pressure regulation setting; a first branch fuel supply line structure, coupled to said inlet portion of said first pressure regulator apparatus for receiving a pressurized first fuel; a second branch fuel supply line structure, coupled to said inlet portion of said first pressure regulator apparatus, for receiving a pressurized second fuel having a wobbe index higher than that of said first fuel; valve apparatus operable to permit flow of only a selectively variable one of said first and second fuels to said inlet portion of said first pressure regulator apparatus and thus to said orificed fuel inlet portion of said fuel burner apparatus, said valve apparatus including first and second electromechanical valves connected in series in said first branch fuel supply line structure in opposite normal flow orientations; and second pressure regulator apparatus connected in said second branch fuel supply line structure and having a second pressure regulation setting, said first and second pressure regulation settings being related to one another in a predetermined manner such that, without altering said orificed fuel inlet portion of said burner apparatus, the firing rate of said burner apparatus will remain essentially constant regardless of which of said first and second fuels is being supplied thereto.
 12. The fuel-fired heating appliance of claim 11 wherein: said fuel-fired heating appliance is a dual fuel boiler.
 13. The fuel-fired heating apparatus of claim 11 wherein: said burner apparatus comprises a plurality of non-aspirating type fuel burners each having an orificed inlet.
 14. The fuel-fired heating appliance of claim 11 wherein: said first pressure regulation apparatus comprises a plurality of pressure regulator devices.
 15. The fuel-fired heating appliance of claim 11 wherein: said first pressure regulation setting is greater than said second pressure regulation setting.
 16. A fuel-fired heating appliance comprising: fuel burner apparatus having an inlet portion; and fuel delivery apparatus operative to deliver to said fuel burner apparatus a selectively variable one of a first fuel from a source thereof, and a second fuel from a source thereof, said fuel delivery apparatus including a main fuel supply line connected to said inlet portion of said fuel burner apparatus, a first fuel supply branch line connected to said main fuel supply line and connectable to said first source, first valve apparatus connected in said first fuel supply branch line and being openable and closable to selectively permit and preclude flow of said first fuel therethrough, said first valve apparatus including first and second electromechanical two position, two-way valves connected in series, and in opposite normal flow orientations, in said first fuel supply branch line, a second fuel supply branch line connected to said main fuel supply line and connectable to said second source, and second valve apparatus connected in said second fuel supply branch line and being openable and closable to selectively permit and preclude flow of said second fuel therethrough.
 17. The fuel-fired heating appliance of claim 16 wherein: said fuel-fired heating appliance is a dual fuel boiler.
 18. The fuel-fired heating appliance of claim 16 wherein: said first fuel is natural gas, and said second fuel is propane. 